> On 05/13/2010 11:05 AM, KOSAKI Motohiro wrote:
> >>>> void *kvmalloc(size_t size)
> >>>> {
> >>>> void *ptr;
> >>>>
> >>>> if (size < PAGE_SIZE)
> >>>> return kmalloc(PAGE_SIZE, GFP_KERNEL);
> >>>> ptr = alloc_pages_exact(size, GFP_KERNEL | __GFP_NOWARN);
> >>>
> >>> low order GFP_KERNEL allocation never fail. then, this doesn't works
> >>> as you expected.
> >>
> >> Hi, I suppose you mean the kmalloc allocation -- so kmalloc should fail
> >> iff alloc_pages_exact (unless somebody frees a heap of memory indeed)?
> >
> > I mean, if size of alloc_pages_exact() argument is less than 8 pages,
> > alloc_pages_exact() never fail. see __alloc_pages_slowpath().
>
> Sorry, I don't see what's the problem with that. I can see only that
> alloc_pages_exact is superfluous there as kmalloc "won't fail" earlier.
I don't talk about kmalloc. it's ok to never fail. but low order alloc_pages_exact() never fail too.
Is this ok? Why?
> >>>> if (ptr != NULL)
> >>>> return ptr;
> >>>>
> >>>> return vmalloc(size);
> >>>
> >>> On x86, vmalloc area is only 128MB address space. it is very rare
> >>> resource than physical ram. vmalloc fallback is not good idea.
> >>
> >> These functions are a replacement for explicit
> >> if (!(x = kmalloc()))
> >> x = vmalloc();
> >> ...
> >> if (is_vmalloc(x))
> >> vfree(x);
> >> else
> >> kfree(x);
> >> in the code (like fdtable does this).
> >>
> >> The 128M limit on x86_32 for vmalloc is configurable so if drivers in
> >> sum need more on some specific hardware, it can be increased on the
> >> command line (I had to do this on one machine in the past).
> >
> > Right, but 99% end user don't do this. I don't think this is effective advise.
>
> Indeed. I didn't mean that as the users should change that. They should
> only if there is some weird hardware with weird drivers.
>
> >> Anyway as this is a replacement for explicit tests, it shouldn't change
> >> the behaviour in any way. Obviously when a user doesn't need virtually
> >> contiguous space, he shouldn't use this interface at all.
> >
> > Why can't we make fdtable virtually contiguous free?
>
> This is possible, but the question is why to make the code more complex?
because it's broken. Or Am I missing something?
> > Anyway, alloc_fdmem() also don't works as author expected.
>
> Pardon my ignorance, why? (There are more similar users:
> init_section_page_cgroup, sys_add_key, ext4_fill_flex_info and many others.)
I think init_section_page_cgroup is ok. it's called at boot time. we don't enter forever page reclaim.
but other case, I don't know the reason. I guess they also have specific assumption.
I only said, generically it isn't right.
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
